The human eye provides a foveal characteristic of vision. The central region of the retina, the fovea, is capable of interpreting higher resolution imagery, greater detail, than surrounding regions of the retina. Visual acuity of the retina falls off further from the fovea, as the foveal angle increases. Consequently, the human eye resolves high resolution at the center of the field of view and continually decreasing resolution at greater peripheral areas of the field of view. This high-resolution central field of view and lower-resolution peripheral field of view can be described as the foveated characteristic of vision.
Some prior visual displays have attempted to take advantage of the foveated characteristics of human vision. Because peripheral vision does not see high resolution, there is no reason to use a high density of pixels in the periphery of the visual display. However, peripheral vision is sensitive to movement in changes and intensity, therefore, it is important to retain peripheral vision as an early-warning or indication of approaching hazards, rather than only displaying a narrow field of view. Generally, visual displays which can benefit from the foveated characteristics of human vision are near-eye or head-mounted visual displays.
Some of the benefits of employing foveated visual displays include increasing the field of view, decreasing the total image data and associated bandwidth required to present high resolution only at the center of an image and low resolution in the periphery, and lower computer system dependency allowing for faster refresh rates of images on the visual display and increased complexity of the visual data being displayed.
Some previous displays attempted to create foveated images using optical systems such as U.S. Pat. No. 5,808,589 to Fergason and U.S. Pat. No. 6,222,675 to Mall et al. Other existing visual display systems attempted to create foveated images using software interpolation techniques that reduce the pixel resolution at increasing peripheral regions of the image being displayed by clustering pixels in the periphery of a display. Two examples are U.S. Pat. No. 5,071,209 to Chang et al. and U.S. Pat. No. 5,726,670 to Tabata et al. However, each of these visual display systems suffer from a reliance upon a redundancy of image information being presented to the viewer or the computer system. For example, in the Mall et al. '675 patent one eye of the viewer sees the entire field of view in low resolution and another eye of the viewer sees the central region of the field of view in high resolution. The user interprets this as a combined visual display with high resolution at the center and low resolution on the periphery. A similar effect is presented in the Fergason '589 patent where a high-resolution central image overlays a wide field of view, low-resolution image. The redundancy of both of these systems requires increased circuitry and a higher data load on any associated computer processing system. An additional disadvantage of primarily ocular systems is the substantial complexity, size, and weight of the components required for such a system.
Furthermore, existing near-eye visual displays that rely upon optical projection systems or flat computer generated displays often cause discomfort for the viewer because they fail to accommodate the severe angle between the eyes and peripheral images on the display. One method proposed to correct this problem is varying the horizontal width of pixels as disclosed in U.S. Pat. No. 6,115,007 to Yamazaki. A disadvantage of the Yamazaki '007 patent is the need to adjust the pixel width on existing flat panel visual displays, requiring an additional step of software image interpolation. Furthermore, existing near-eye displays have substantial disadvantages including excessive and awkward weight and small viewing screens.